Fracture Toughness Investigations of Metal Matrix Composites Using Compact Specimens

This paper presents experimental results of the fracture toughness tests carried out on metal matrix composites. The material was produced using the 44200 aluminium alloy reinforced by Al2O3 in the form of Saffil fibres. Three different contents of Al2O3 were taken into account, i.e. 10%, 15%, 20%. The main aim of the research was to examine an influence of the aluminium oxide content on a critical value of the stress intensity factor, KIC. All tests were performed using a miniature compact specimen, which was four times smaller than the typical one. The results of FEA analysis confirmed a typical distribution of the effective stress at the tip of the notch. In each test the composite specimen was mounted in the loading system of the testing machine by applying special grips. Crack tip opening displacement of the specimen notch was measured by means of the clip on knife edge extensometer having 10mm gauge length. The results in form of tensile force versus crack tip opening displacement show the first mode of fracture. An inspection of the pre-cracked zone of the composite did not exhibit the typical features usually observed on specimen surface after fatigue. An influence of the Al2O3 Saffil fibres content within the range from 10% to 20% on a critical value of the stress intensity factor was negligible small. The KIC of the composites tested in this research achieved the level of 12 MPa m1/2.